1. Field of the Invention
The present invention relates to giant magnetoresistive (GMR) devices that contain a GMR sensor element, which may be used in GMR sensors, spin valves, and magnetic memories. The present invention relates more particularly to a GMR device having enhanced magnetoresistive resistivity sensitivity, and a method of fabricating the same.
2. Description of Related Art
For over 2000 years, magnetic sensors have been beneficially deployed in navigation equipment for sensing the Earth's magnetic poles. Current magnetoelectronic devices may be used in medical applications for magnetic resonance imaging; in military surveillance for detecting submarines and buried landmines; in highway toll systems for traffic detection of vehicles for automated-toll-pay systems; in disk drives as magnetic pickup heads; in magnetoelectronics memories for Magnetic Random Access Memories (MRAM); and in automated industrial equipment for proximity sensors.
Magnetoelectronics devices may be used to measure the presence, magnitude, and/or direction of a magnetic field, changes in a magnetic field due to a presence of a ferromagnetic object, characteristics of the Earth's field, and electrical current flow. Many different types and constructions of magnetoelectronic devices exist. The types and constructions are generally dictated by the sensing technology, and the detectable magnetic field. Accurately and reliably measuring magnetic fields smaller than the Earth's field may present an obstacle for many magnetoelectronic devices, and thus, may limit the type and construction of the magnetoelectronic devices. One such device that appears to overcome these obstacles is a magnetosensor that employs the giant magnetoresistive (GMR) effect. Magnetosensors that employ the GMR effect may be capable of measuring small fields from magnetized objects, electrical currents, deviations in the Earth's magnetic field, and non-magnetized objects.
Reportedly, as a result of recent advances in the art of thin-film material processing, the giant magnetoresistive (GMR) effect was discovered in 1988 by Baibich et al. The GMR effect describes the phenomenon of dramatic resistance drop in certain materials in the presence of magnetic fields. This change in resistance divided by the total resistance of the GMR device may be defined as the magnetoresistive (MR) resistivity sensitivity of the GMR device.
At the core of many GMR magnetoelectronic devices is a GMR sensor element. The GMR sensor element may be used as the foundation for GMR magnetoelectronic devices, including unpinned sandwiches, antiferromagnetic multilayers, and antiferromagnetic pinned spin valves. Generally, this GMR sensor element is constructed in a stack configuration in which the stack contains a number of deposited layers of thin-film materials. Common to most GMR sensor elements, the minimum number of layers in the stack usually includes three layers—two magnetic layers separated by at least one conductive nonmagnetic spacer layer. It is believed that the MR resistivity sensitivity of the tri-layer and other multilayer stacks is a function of the thickness of the stack's spacer layers and the phenomenon of spin-dependent scattering of conduction electrons at the boundaries between the spacer layers and the magnetic layers.
In the absence of an external magnetic field, the magnetic layers in a tri-layer stack configuration may exchange magnetic coupling. This coupling may oscillate between ferromagnetically coupling and antiferromagnetically coupling, and may be partially modeled by Ruderman, Kittel, Kasuya, and Yosida theory of magnetic coupling (RKKY coupling).
The antiferromagnetic coupling is believed to cause the magnetic moments of the two magnetic layers to become antiparallel. In this antiparallel state, the stack of materials comprising the GMR sensor element is believed to exhibit maximum spin-dependent scattering of conduction electrons. The maximum spin-dependent scattering of conduction electrons in turn is believed to place the GMR sensor element in a maximum resistance state. By applying an adequate magnetic field to overcome the antiferromagnetic coupling, the antiparallel magnetic moments of the magnetic layers become parallel, thereby decreasing the spin-dependent electrons of the conduction electrons, and likewise, decreasing the resistance in the GMR magnetoelectronic devices. On the other hand, the ferromagnetic coupling is believed to cause the magnetic moments of the two magnetic layers to become parallel, which in turn is believed to exhibit something less than maximum spin-dependent scattering of conduction electrons or a lower resistance state.
Generally, as the spacer layer becomes thin, the MR resistivity sensitivity increases with a given oscillation period. That is, thinner spacer layers may produce larger peak antiferromagnetic coupling during an antiferromagnetic-coupling-oscillation period, and larger peak ferromagnetic coupling during a ferromagnetic-coupling-oscillation period. As the spacer layer thickness diminishes, however, defects in the stack's layers may occur due to processing. Such defects may present themselves as bridging sites or “pin-holes” that cause the magnetic layers to connect or “bridge” to each other, which may dramatically reduce or eliminate any GMR effect. In addition to pin-hole defects, the tri-layer stack may exhibit “waviness” or non-smooth layers. This waviness, non-smoothness or rough texturing is believed to affect the oscillation between the antiferromagnetic coupling and the ferromagnetic coupling, which may be reflected as a shift in the working range of the GMR sensor element. Further, it is believed that the non-smoothness or rough texturing may result in the GMR sensor element exhibiting Néel-type orange peel coupling in addition to the RKKY coupling. Generally, as the spacer layer thickness becomes thin, this Néel-type orange peel coupling may dominate the RKKY coupling causing a high ferromagnetic exchange between the magnetic layers, and causing a shift in the working range of the GMR sensor element to higher fields. Unfortunately, this shift may reduce or adversely affect the MR resistivity sensitivity of the GMR sensor element.
Therefore, what is needed is an enhanced GMR sensor element and method of manufacturing the GMR sensor element that allows for thin spacer layers and that minimizes, eliminates, or “fits” the Néel-type orange peel coupling generally accompanied with thin spacer layers. Further needed is an enhanced GMR sensor element and method of manufacturing the GMR sensor element that minimizes or eliminates an undesired shift in the working range of the GMR sensor element, thereby increasing its MR resistivity sensitivity as compared with un-enhanced GMR sensor elements.